1. Technical Field
The present invention is related to an information recording medium, a method for generating head positioning identification information, a method for determining head positioning in an information recording and reading apparatus, and, particularly, to an information recording medium shaped in the form of a disk and having recorded thereon identification information for determining head positioning, a method for generating head positioning identification information for generating said identification information, a method for determining head positioning when the information recording medium is rotated and the head is moved essentially in the radial direction of the disk, and an information recording and reading apparatus to which the method for determining head positioning is applicable.
2. Description of the Background Art
A plurality of data tracks is concentrically formed on a magnetic disk such as a hard disk or a flexible disk. Reading of information from or writing of information to the magnetic disk is performed after rotating the magnetic disk and moving a magnetic head essentially in the radial direction of the magnetic disk to position the magnetic head at a specific data track (a so-called seek operation). Positioning of the magnetic head at a specific data track is performed by respectively reading identification information and burst patterns which are prerecorded on the magnetic disk with the magnetic head, as described below.
FIG. 8 shows part of the identification information and burst patterns recorded on a magnetic disk. In FIG. 8, the magnetic disk rotates in the circumferential direction thereof (the direction in FIG. 8 indicated by arrow F), and a magnetic head (not shown) moves essentially in the radial direction of the magnetic disk (the direction in FIG. 8 indicated by arrow G). A plurality of data tracks 100A, 100B, 100C . . . on which data is recorded is concentrically formed on the magnetic disk. Each data track is partially disconnected in the circumferential direction, and an identification information recording region 102 and a burst pattern recording region 104 are formed in the portions where the data track is disconnected.
Each data track is assigned a track address for identifying each data track, and, in the identification information recording region 102, identification information of a predetermined number of bits representing the track address of each data track by a gray code (cyclic binary code) is recorded in the circumferential direction so as to correspond to each data track. Also, in the burst pattern recording region 104, a plurality of (in FIG. 8, four) burst pattern trains 106A, 106B, 106C, and 106D is recorded, in which areas having a signal recorded therein (shown by hatching in FIG. 8) are respectively arranged in the radial direction.
To position the magnetic head at a predetermined data track, the magnetic disk is rotated and the magnetic head is moved essentially in the radial direction of the magnetic disk, as described above, and, each time the identification information recording region 102 is made to face the magnetic head by the rotation of the magnetic disk, the track address of the data track faced by the magnetic head is calculated as the current magnetic head position based on the identification information read signal output by the magnetic head. In the identification information, as more specifically shown in FIG. 9(A), the recording length for 1-bit data (L.sub.0 in FIG. 9(A)) is predetermined, and the identification information is recorded so that the portion in the recording extent having length L.sub.0 corresponding to each bit is magnetized to N or S in accordance with whether the value of each bit of the gray code representing the track address is "0" or "1".
For instance, if the magnetic head passes the identification information recording region 102A for data track N shown in FIG. 9(A), a signal in which a pulse occurs at the portions magnetized to N or S, as shown in FIG. 9(B), is output by the magnetic head as an identification information read signal. However, since the magnetic disk is rotating at this point in time and the magnetic head moves essentially in the radial direction of the magnetic disk, the magnetic head actually passes obliquely with respect to the recording direction (the circumferential direction of the magnetic disk) to identification information to be recorded onto the identification recording region 102, as shown by locus 108 in FIG. 9(A). Based on the positioning of the pulses of the identification information read signal, the value of the gray code as identification information recorded in the identification information recording region 102 can be determined, and a track address can be obtained by converting the thus-determined gray code to a binary code.
Incidentally, since identification information is represented by gray code, the values of the respective bits of the identification information of adjacent data tracks are equal except for a predetermined bit. Consequently, as shown in FIG. 9(A) as locus 110, even if the magnetic head passes so as to span the identification information recording regions (in FIG. 9(A), recording regions 102A and 102B) of two adjacent data tracks, the identification information read signal output by the magnetic head corresponds to either of the identification information of the two data tracks (for instance, a gray code "100" corresponding to data track N is output if the magnetic head passes along locus 110). Thus, even if it is taken into consideration that there are two directions in which the magnetic head moves in a seek operation (from the outer peripheral side to the inner peripheral side of the magnetic disk, or from the inner peripheral side to the outer peripheral side), the data track at which the magnetic head is currently positioned can be determined with an error width of one track .+-.1 track (a total of three tracks in width) based on the identification information read by the magnetic head. Then, according to the deviation of the determined data track from the target data track, the movement of the magnetic head is controlled so that the magnetic head faces the target data track.
When it is determined that the magnetic head has faced the target data track, then, based on a plurality of signals obtained when the plurality of burst pattern trains in the burst pattern recording region 104 is read by the magnetic head, respectively, a positioning detection signal having a level linearly varying according to the head position is generated, and, based on the positioning detection signal, the magnetic head is positioned so that the center of the magnetic head gap is positioned at the width center of the target data track.
Regarding the magnetic disk, there is a constant demand for an increase in the storage capacity and the shortening of the access time for recording or reading information. The increase in the storage capacity can be attained by decreasing the data track spacing and increasing the information recording density, while the shortening of the access time can be attained by moving the magnetic head at a high speed in the seek operation.
However, this causes a large angle .theta. (refer to FIG. 9(A)) to be formed between the locus drawn by the magnetic head passing over the identification information recording region 102 and the recording direction of identification information onto the identification information recording region 102 (the circumferential direction of the magnetic disk), which produces a problem in that identification information cannot be correctly read by the magnetic head and hence the magnetic head position cannot be accurately determined.
By way of example, if the magnetic head passes over data tracks N, N+1, N+2 so as to span the identification information recording regions 102A to 102C for data track N to data track N+2 as locus 112 (FIG. 9(A)) and identification information read signal as shown in FIG. 9(C) is output, the gray code represented by this signal is "101", and, by converting this to binary, "110" which is different from the track address of any of data track N to data track N+2 is obtained, a misconception of magnetic head positioning occurs.
More accurately, if it is assumed that the number of bits of identification information is n, this misconception of magnetic head positioning occurs in the event that, when the magnetic disk is rotated and the magnetic head is moved in the radial direction of the magnetic disk, the relative position between the magnetic head and the magnetic disk changes by one or more track widths in the radial direction of the magnetic disk while the relative position changes by the recording length of identification information of n-1 bits in the circumferential direction of the magnetic disk. In this case, depending on the positional relationship between the magnetic head and the identification information recording regions, the magnetic head passes so as to span three or more data tracks as shown in FIG. 9(A) as locus 112, and thus an identification information read error and misconception of magnetic head positioning occur.